I have 1G bowls for most of my boys. They are cheap and easy to clean. The only downside is I can't heat them, so I am now looking for a solution for the winter.
Ideally, I think bettas would prefer at least 2.5G. My 1G boys do ok, they are all healthy and active, but I would like to give them more room.
I have an L shaped desk, currently home to 6 1G betta bowls, 1 1G Planet Aquarium tank and a 5G tank. It is crowded, but I could probably fit one or 2 more if I tried.
I would NEVER use a breeding trap for my boys. They use them at the lfs sometimes for their more pricey bettas. They get sold quickly, but to see them in such a tiny space sucks big time. The reason they use them is to move them off the shelf faster. Their betta display is off to one side, so most people don't see them when they are looking at fish, you have to know it is there.
I got my Kaz out of a breeding trap, thank goodness he is tiny and was still able to move around, the bigger ones aren't so lucky.